In an electronic device such as a semiconductor element, semiconductor parts such as transistors, resistors and the like are generally arranged on a substrate. Those parts must be electrically insulated from each other, and hence it is necessary to provide areas among the parts so as to separate them. Those areas are referred to as “isolation areas”, which have been hitherto generally provided by forming an insulating film selectively on the surface of a semiconductor substrate.
Meanwhile, in the field of electronic devices, the density and integration degree have been increased in recent years. According to the increase of the density and integration degree, it has become difficult to form isolation structures minute enough to meet the needed integration degree and hence it has been required to develop new isolation structures satisfying the needs. Those new isolation structures include a trench isolation structure, which is formed by carving fine trenches on the surface of a semiconductor substrate and then filling the trenches with insulating material so as to electrically separate a part positioned on one side from another part on the other side of each trench. The structure thus separating the parts can reduce the isolation area, as compared with the conventional structures, and is accordingly effective in achieving the high integration degree required in these days.
As a method for forming the above trench isolation structure, a process is studied in which a polysilazane composition is applied and then converted into silicon dioxide (e.g., Patent documents 1 and 2). This process generally comprises the steps of: applying a polysilazane composition onto a substrate surface having a trench structure, so as to fill the trenches with the composition; hardening the composition by curing or the like, so as to convert polysilazane into silicon dioxide; and then removing excess of the silicon dioxide formed on the surface by chemical mechanical polishing (hereinafter, referred to as “CMP”).
However, insulating films formed by conventional methods often cannot fully fulfill their functions because very high precision is required to produce recent semiconductor elements. For example, in the case where the substrate surface has trenches of high aspect ratios, polysilazane is often insufficiently oxidized in the trenches. That is because, although enough amounts of oxygen and moisture are necessary to oxidize polysilazane, they are often insufficiently supplied to polysilazane in the trenches, particularly, at the bottoms (which are distant from the surface) in the deep trenches. Consequently, the resultant structure is densified so insufficiently that it cannot be successfully fabricated as designed in the wet-etching treatment and the like performed later.
Further, isolation structures other than the trench isolation structure are also required to be made more precise. However, there are rooms for improvement in insulating films and the like formed by conventional methods. Specifically, for example, in the case where a polysilazane-containing composition is applied and hardened to form an inter-metal dielectric film or a pre-metal dielectric film on the surface of a substrate, problems of cracks in the film and/or of crystal defects at the interface are often caused by large volume shrinkage in the course of hardening.